1. Field of the Invention
The present invention relates to a fuel pump for sucking a fuel from a fuel tank and discharging, suitable for use in an internal combustion engine.
2. Description of Related Art
FIG. 4 shows a conventional fuel pump having a disk-like impeller including blades at the outer periphery thereof. The impeller rotates to suck and discharge a fuel. An impeller 110 is rotatably provided between an upper housing 100 and a lower housing (not illustrated). The lower housing includes a fuel inlet at a position facing an inlet position 105 of the upper housing 100. The upper housing 100 includes an arc-shaped pump groove 101 along blades of the impeller 110 from the inlet position 105 to a fuel outlet 106. The lower housing also includes a pump groove facing the pump groove 101. Both pump grooves form a pump fluid passage 102.
However, in the conventional fuel pump, a cross sectional area of the pump groove sharply decreases at the fuel outlet, and the pump groove 101 ends at the fuel outlet 106. Thus, fuel held in a blade groove formed between each of adjacent blades of the impeller 110 collides with a wall surface 107 of the upper housing 100, which is positioned at the end of the pump fluid passage 102 and forms the fuel outlet 106, thereby introducing a noise of which frequency is expressed by (the number of impellers)xc3x97(motor rotation number).
U.S. Pat. No. 5,011,367 discloses a fuel pump in which a pump groove crosses an impeller, and the wall surface of the pump groove is rounded to reduce a noise. JP-A-9-119390 discloses a fuel pump in which a gap between the outer periphery of an impeller and a circumferential wall surface facing the outer periphery of the impeller gradually decreases to reduce a noise.
However, in both U.S. Pat. No. 5,011,367 and JP-A-9-119390, a pump groove ends at a fuel outlet. Thus, even when the pump groove is rounded, or the gap between the outer periphery of the impeller and the circumferential wall is gradually decreased, fuel held in the blade groove might collide with a wall surface forming the fuel outlet to introduce the noise.
U.S. Pat. No. 5,498,124 discloses a fuel pump in which a damping portion is formed at the downstream side of discharge port. The damper portion includes a slanting wall surface going away from the outer periphery of an impeller in the rotating direction of the impeller.
An object of the present invention is to reduce a noise in a fuel pump.
According to a first aspect of the present invention, depth, and outer and inner diameters of a pump groove starts to gradually change from a fuel upstream side of a fuel outlet. The depth of the pump groove gradually decreases, the outer diameter of the pump groove gradually decreases to approach an outer diameter of the impeller, and the inner diameter of the pump groove gradually increases to approach the outer diameter of the impeller. The pump groove ends at a downstream side of the fuel outlet.
Thus, the fuel held in a blade groove passes through the fuel outlet, and does not collide with a wall surface of the fuel outlet, thereby reducing a noise at the fuel outlet.
According to a second aspect of the present invention, a buffer chamber is formed at a fuel downstream side of the fuel outlet in a rotating direction of the impeller. The buffer chamber communicates with the pump groove, and a cross sectional area thereof decreases in the rotating direction of the impeller. Inner and outer walls of the buffer chamber gradually approach the outer periphery of the impeller in the rotating direction of the impeller. An end point of the buffer chamber is arranged at a position substantially corresponding to the outer diameter of the impeller.
Thus, when the impeller passes through a fuel downstream side end of the fuel outlet while providing a slight gap therebetween, amount of the fuel around a fluid passage end, which transmits the noise, is reduced, thereby suppressing the noise. The fuel is pushed out from the buffer chamber to be discharged through the fuel outlet.